>>There is nothing loading the bundles.
>>
>>>They are loaded in the Bundles.config
>
>Okay... here is bundles config:
>
>

>  public static void RegisterBundles(BundleCollection bundles)
>        {
>            bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
>                        "~/Scripts/jquery-{version}.js"));
>
>            bundles.Add(new ScriptBundle("~/bundles/jqueryui").Include(
>                        "~/Scripts/jquery-ui-{version}.js"));
>
>            bundles.Add(new ScriptBundle("~/bundles/jqueryval").Include(
>                        "~/Scripts/jquery.unobtrusive*",
>                        "~/Scripts/jquery.validate*"));
>
>            // Use the development version of Modernizr to develop with and learn from. Then, when you're
>            // ready for production, use the build tool at http://modernizr.com to pick only the tests you need.
>            bundles.Add(new ScriptBundle("~/bundles/modernizr").Include(
>                        "~/Scripts/modernizr-*"));
>
>            bundles.Add(new ScriptBundle("~/bundles/bootstrap").Include(
>                      "~/Scripts/bootstrap.js",
>                      "~/Scripts/respond.js"));
>
>            bundles.Add(new StyleBundle("~/Content/css").Include(
>                      "~/Content/bootstrap.css",
>                      "~/Content/site.css"));
>
>            bundles.Add(new StyleBundle("~/Content/themes/base/css").Include(
>                     "~/Content//themes/base/jquery.ui.core.css",
>                     "~/Content//themes/base/jquery.ui.resizable.css",
>                     "~/Content//themes/base/jquery.ui.selectable.css",
>                     "~/Content//themes/base/jquery.ui.accordion.css",
>                     "~/Content//themes/base/jquery.ui.autocomplete.css",
>                     "~/Content//themes/base/jquery.ui.button.css",
>                     "~/Content//themes/base/jquery.ui.dialog.css",
>                     "~/Content//themes/base/jquery.ui.slider.css",
>                     "~/Content//themes/base/jquery.ui.tabs.css",
>                     "~/Content//themes/base/jquery.ui.datepicker.css",
>                     "~/Content//themes/base/jquery.ui.progressbar.css",
>                     "~/Content//themes/base/jquery.ui.theme.css"));
>

>
>
>And then I made changes to render the bungles:
>

>~!doctype html~
>
>~html lang="en"~
>    ~head~
>        ~meta charset="utf-8"~
>        ~title~accordion demo~/title~
>        @Styles.Render("~/Content/css")
>        @Styles.Render("~/bundles/modernizr")
>        @Styles.Render("~/bundles/jquery")
>        @Styles.Render("~/bundles/jqueryval")
>        @Styles.Render("~/bundles/jqueryui")
>        @Styles.Render("~/Content/themes/base/css")
>
>       ~script~
>            $(function () {
>                $("#accordion").accordion();
>            });
>        ~/script~
>    ~/head~
>    ~body~
>        ~div class="row"~
>            ~div id="accordion"~
>                ~h3~Section 1~/h3~
>                ~div~
>                    ~p~
>
>                        Mauris mauris ante, blandit et, ultrices a, suscipit eget, quam. Integer
>                    ~/p~
>                ~/div~
>
>                ~h3~Section 2~/h3~
>                ~div~
>                    ~p~
>                        Sed non urna. Donec et ante. Phasellus eu ligula. Vestibulum sit amet
>                    ~/p~
>                ~/div~
>                ~h3~Section 3~/h3~
>                ~div~
>                    ~p~
>                        lacinia ornare, quam ante aliquam nisi, eu iaculis leo purus venenatis dui.
>                    ~/p~
>                    ~ul~
>                        ~li~List item one~/li~
>                    ~/ul~
>                ~/div~
>                ~h3~Section 4~/h3~
>                ~div~
>                    ~p~
>                        Cras dictum. Pellentesque habitant morbi tristique senectus et netus
>                    ~/p~
>                    ~p~
>                        inceptos himenaeos.
>                    ~/p~
>                ~/div~
>            ~/div~
>        ~/div~
>     ~/body~
>~/html~
>
>

>
>
>And now the error changes:
>
>Unhandled exception at line 111, column 5 in http://localhost:64779/Home/Index
>0x800a1391 - JavaScript runtime error: '$' is undefined

Move modernizr after loading jquery. Also, can you view the source (View Source) and see if your js files are loaded correctly? That error indicates your jquery is not loaded.